Originated from the phrase "sloppy seconds". Shitty seconds is the act of taking a shit in the same toilet within a couple minutes after someone else whether the first shitter flushed the toilet or not. The bathroom still smells like shit from the previous shitter and the toilet seat is already warmed up for you. Sometimes, if you are lucky enough, you will even find left over pubic hairs from the previous shitter as an added bonus.

Vuhgena (as she's leaving the bathroom), "Aww okay I'm done."

Antwan, "Damnit I hate shitty seconds! The toilet seat is all warm and it feels weird! I thought girls can't poop!? I mean it smells like shit in here and she got pubic hair everywhere! OMFG is that a used tampon on the floor??"